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Programmer’s Reference Manual 93
AC ’97 Modem Controller Registers (D30:F3)
3.1.9 HEADTYP—Header Type Register (Modem—D30:F3)
Address Offset: 0Eh Attribute: RO
Default Value: 00h Size: 8 bits
Lockable: No Power Well: Core
3.1.10 MMBAR—Modem Mixer Base Address Register
(Modem—D30:F3)
Address Offset: 10–13h Attribute: R/W, RO
Default Value: 00000001h Size: 32 bits
The Native PCI Mode Modem uses PCI Base Address register #1 to request a contiguous block of
I/O space that is to be used for the Modem Mixer software interface. The mixer requires 256 bytes
of I/O space. All accesses to the mixer registers are forwarded over the AC-link to the codec where
the registers reside.
In the case of the split codec implementation, accesses to the different codecs are differentiated by
the controller by using address offsets 00h
–7Fh for the primary codec and address offsets 80h–FEh
for the secondary codec.
Bit Description
7:0 Header Type — RO.
Bit Description
31:16 Hardwired to 0’s.
15:8
Base Address — R/W. These bits are used in the I/O space decode of the Modem interface
registers. The number of upper bits that a device actually implements depends on how much of the
address space the device will respond to. For the AC ‘97 Modem, the upper 16 bits are hardwired to
0, while bits 15:8 are programmable. This configuration yields a maximum I/O block size of
256 bytes for this base address.
7:1 Reserved. Read as 0
0 Resource Type Indicator (RTE) — RO. Hardwired to 1 indicating a request for I/O space.